when your drive first spins, it hits its peak RPM. In a raid0 setup the data is split between the two drives so that when a particular piece of data is being accessed it is being pulled from drive A a little bit, then drive B a little bit. This way peak RPM is constantly delivered.

It was introduced before SSDs. I personally feel like it's a bit redundant now if you've got a large SSD for all your games and OS.